ACDC, the abbreviation of “Application specific Congestion control for Data Communication”, is an access control mechanism, and an operating company may allow or block an access request of specific application software when UE (terminal) is in an idle state. ACDC is only applicable to UE in an idle state and inapplicable to UE in a connected state. ACDC plays a role in reducing an overload of an access network or a core network.
It has the following basic characteristics.
1) ACDC is applicable to a Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (URAN) and an Evolved UTRAN (E-UTRAN).
2) A home network configures at least four ACDC categories corresponding to applications defined by an operating company respectively for UE.
3) Enabling an ACDC category in the UE is a responsibility of the home network, and how to categorize is not defined by the 3rd Generation Partnership Project (3GPP).
4) The UE has a set of mechanism to verify that it is a trusted source enabling the ACDC category for it.
5) A service network broadcasts control information on an access network side, including: blocking information of each ACDC category and whether roaming UE should be limited to ACDC or not.
6) Blocking information broadcast in each cell is different, and a corresponding relationship between an application in the UE and an ACDC category is configured by the home network.
7) The UE may determine whether to allow transmission of an access request of a specific application on the basis of the broadcast blocking information and an ACDC category configuration in the UE.
8) The service network should indicate ACDC at the same time of executing other access control, and when ACDC and Access Class Barring (ACB) are indicated at the same time, ACDC should cover ACB.
9) When multiple core networks share the same access network, the access network should be capable of independently executing ACDC for different core networks respectively. For alleviating congestion of a shared access network and for fairness, the same blocking rate should be set for different operating companies.
ACDC Category Configuration
An operating system of UE allocates an application software Identity (id) for each piece of application software, and the UE obtains a corresponding relationship between the application software ids and ACDC categories by receiving a broadcast of a home network or by virtue of remote Subscriber Identity Module (SIM) card writing of an core network. Multiple different application software ids may correspond to the same ACDC category.
The home network configures the ACDC application categories for the UE:
1: an application which is limited least (with a highest access priority) is configured into a highest ACDC category, i.e. ACDC #1;
2: an application which is limited more than ACDC #1 is configured into a second highest ACDC category, i.e. ACDC #2, and so on; and
3: an application which is limited most (with a lowest access priority) is configured into a lowest ACDC category, or is configured into no ACDC category.
The application which is configured into no ACDC category on the UE should be considered by the UE to be the lowest ACDC category. When ACDC is used, a service network broadcasts blocking information, and the blocking information is sent sequentially from the highest to lowest ACDC categories. The home network and the service network may use different categorization methods. The service network determines whether to apply ACDC to roaming UE or not.
A number of ACDC categories on UE may be different from a number of ACDC categories broadcast by a service network. Such a circumstance may occur when the UE roams, and the number of the ACDC categories broadcast by the service network is different from a home network of the UE. For such a circumstance, the following strategies are adopted.
A: when the number of the ACDC categories broadcast by the service network is more than that configured by the UE, the UE uses blocking information corresponding to ACDC, adopts blocking information of a lowest category in a broadcast of a serving cell for an uncategorized application, and ignores other blocking information mismatched with own ACDC category.
B: when a number of ACDC categories corresponding to blocking information broadcast by the service network is smaller than own configuration of the UE, the UE adopts the corresponding blocking information for a matched ACDC category, and adopts blocking information of the lowest category in the serving cell for another application.
It is important to note that a matched ACDC category refers to that an ACDC category sequence of blocking information broadcast by the service network is the same as an ACDC category sequence configured by the UE.
ACDC Process in a Service Network
The service network sequentially broadcasts ACDC blocking parameters of different categories, including a “blocking time” and a “blocking probability”.
The blocking time: when an ACDC category corresponding to application software a is #1 and a broadcast blocking time of ACDC #1 is 100 ms, once a connection request of the application software a is blocked by an ACDC strategy, the connection request of the application software 2 will always be blocked within the blocking time 100 ms.
The blocking probability: when an ACDC category corresponding to application software b is #2 and a broadcast blocking probability of ACDC #2 is 0.6, when the application software b initiates a connection request, UE generates a random number between 0-1 for it, when the random number is smaller than or equal to 0.6, access is allowed, and when it is larger than 0.6, access is rejected.
ACDC executes access control for different application software, but ACDC has the following shortcoming.
ACDC may make an admission judgment only in an idle state. When there is an application allowed to access a network, no more ACDC judgment will be made before Radio Resource Control (RRC) is disconnected, and another application with a low priority may directly access the network without ACDC judgments. This is unfavorable for respective management and control over different application software and unfavorable for fairness of priorities between applications.